The conventional Hellfire missile seeker acquires (locates) a target in a given scene by the use of a four-quadrant PIN photodiode detector to detect, in temporal sequence, the laser pulses that are reflected by the target upon being illuminated by a laser designator. FIG. 1 illustrates a typical setting for such Hellfire seeker use. These temporally-detected pulses exist in the near infrared (1.06 micrometer) spectral band and are processed in accordance with the well-known principle of semi-active laser (SAL) last pulse logic (LPL). The SAL Hellfire seeker acquires the designated target by analyzing the reflected laser pulse returns that are detected by the photodiode detector, generating a decoder gate and further analyzing the laser pulse returns which occur inside this gate to find the last laser pulse that is representative of the designated target. To wit, a detection threshold based on pulse amplitude of the received laser pulses is established by the pulse discriminator 107 and sample-and-hold 105. Upon receipt of the first temporally detected laser pulse from photodiode detector 101, a detection threshold based on the amplitude of the first pulse normalizer pulse, PN1, is established. This threshold decays at a constant rate. Only laser pulses among those detected by the photodiode detector which break this decaying threshold, as illustrated in FIG. 2A, are determined to be viable target laser pulses and the last pulse breaking the threshold is deemed to be the correct or true target laser pulse. Within the semi-active laser decoder gate, shown in FIG. 2A, which is established based on pulse repetition frequency codes, three laser pulse returns are shown any of which may have originated from an active source. Of the three pulse returns, only two break the threshold and the second pulse normalizer pulse, PN2, is identified by the photodiode detector as the last pulse. Also well-known is the technology of midwave (3-5 micrometers) imaging infrared (I.sup.2 R) staring focal plane array (FPA) which can respond down to the near infrared (IR) at 1.06 micrometers. Various detector materials such as indium antimonide (InSb) and mercury cadmium telluride (MCT) are viable candidates for the FPA. Suitable InSb FPA's are available from, among others, Amber and Cincinnati Electronics and MCT FPA's may be obtained from the Boeing Company.
Attempts have been made previously to combine the semi-active laser (SAL) and the imaging infrared (I.sup.2 R FPA) guidance concepts to create a dual-mode system where each waveband, independently of each other, processes scene information for targets within the target scene and generates guidance commands for guiding the missile after identifying the true target to track. In such a system, each waveband may complement the other to help acquire the true target but there is no spatial/temporal correlation of target information between the two different wavebands.